1. Field of the Invention
The present invention relates to a device for controlling an automatic transmission and an engine for vehicles by using a fluid clutch and a direct drive mechanism. More particularly, the invention relates to a device for controlling an automatic transmission and an engine for vehicles capable of improving drivability by suppressing shocks at the time of acceleration or deceleration.
2. Prior Art
There has heretofore been known a device for controlling an automatic transmission and an engine for vehicles in which the output torque of an engine is transmitted to the wheels via a torque converter made up of a fluid clutch as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 262169/1993.
FIG. 5 is a diagram schematically illustrating the constitution of major portions of a conventional device for controlling an automatic transmission and an engine for vehicles.
In FIG. 5, an output shaft 1a of an engine 1 mounted on a vehicle is directly coupled to an automatic transmission 2, and the output torque of the engine 1 is transmitted to the wheels (not shown) via the automatic transmission 2.
The automatic transmission 2 includes a torque converter 3 for transmitting the output torque of the engine 1 to the wheels via a fluid, and a direct drive mechanism 4 for directly coupling an output shaft 3a of the torque converter 3 to the output shaft 1a of the engine.
The output torque of the torque converter 3 is transmitted to the wheels via speed-change gears (not shown) in the automatic transmission 2.
The direct drive mechanism 4 is controlled by a direct drive torque control means 5. In a direct drive mode in a steady operation condition, the direct drive control duty D decreases and the fluid on the side of the engine 1 is drained, so that the output shaft 3a of the torque converter 3 is directly coupled to the output shaft 1a of the engine.
An automatic transmission control means 6 constituted by a microcomputer fetches operation condition data from a variety of sensors (not shown), controls the direct drive mechanism 4 through the direct drive torque control means 5 and, further, controls the automatic transmission 2.
The operation of the conventional device for controlling the automatic transmission and the engine for vehicles will now be described with reference to FIG. 5.
When the direct drive mechanism 4 is not working, the torque converter 3 in the automatic transmission 2 transmits the output torque of the engine 1 to the side of the speed-change gears via the fluid, i.e., ATF (AT fluid) filled therein.
The torque converter 3 having a torque amplification function works to increase the drive torque to become greater than the output torque of the engine 1.
Besides, since the output torque of the engine 1 is transmitted to the speed-change gears via the fluid in the automatic transmission 2, a sudden change in the output torque of the engine 1 is absorbed by the fluid; i.e., the input torque to the speed-change gears does not suddenly change, and a shock is avoided.
The torque converter 3 having the above-mentioned advantage also involves a problem as described below.
That is, since the output torque is transmitted via the fluid, heat is generated resulting in an increased transmission loss of energy and an increased fuel consumption.
In order to improve fuel efficiency of the vehicles, therefore, it is accepted practice to provide the automatic transmission 2 with the direct drive mechanism 4 so that, in the steady operation condition, the output shaft 1a of the engine 1 is directly coupled to the output shaft 3a of the torque converter 3 through the direct drive torque control means 5 and that the output torque of the engine 1 is directly transmitted to the side of the speed-change gears. This helps improve the efficiency for transmitting the output torque of the engine 1 and improve the fuel efficiency of vehicles.
In recent years, furthermore, it is a tendency to widen the region for operating the direct drive mechanism 4 as much as possible in an effort to improve the fuel efficiency.
However, when the output torque of the engine 1 suddenly changes at the time of acceleration or deceleration due to the accelerator pedal work, a change in the torque of the engine 1 is directly transmitted from the automatic transmission 2 to the drive axle of the wheels since the direct drive mechanism 4 is directly coupled, giving rise to the occurrence of a shock due to acceleration or deceleration.
When the directly coupled state is maintained during the acceleration, furthermore, the torque converter 3 does not work to amplify the torque; i.e., the drive torque for the wheels is not sufficient and the acceleration becomes poor.
Moreover, despite it is attempted to reset the directly coupled state of the direct drive mechanism 4 at the time when the accelerator pedal is depressed, a delay of transmission occurs through the fluid pressure (hydraulic) passage, and the directly coupled state is not readily reset.
In this case, the output torque of the engine 1 changes due to the depression of the accelerator pedal before the directly coupled state is really reset, and the above-mentioned inconvenience occurs.
In the region where the above-mentioned inconvenience occurs, therefore, it is not allowed to widen a range in which the direct drive mechanism 4 works.
In the conventional device for controlling the automatic transmission and the engine for vehicles as described above, it is not allowed to properly control the direct drive mechanism 4 in the automatic transmission 2. Therefore, the function for amplifying the torque of the torque converter 3 is not exhibited when the direct drive mechanism 4 maintains the directly coupled state at the time of acceleration, arousing a problem in that the drive torque is not sufficient and the acceleration is poor.
Besides, no means is provided for compensating a delay in the operation of the direct drive mechanism 4. Accordingly, despite the direct drive mechanism 4 is reset in response to the operation for depressing the accelerator pedal, the directly coupled state is not readily reset due to a delay in the transmission through the fluid pressure passage. Consequently, the output torque of the engine 1 changes due to the depression of the accelerator pedal before the directly coupled state is reset making it, after all, difficult to suppress the shock caused by a change in the torque during the transient operation condition.
Besides, due to the above-mentioned inconvenience, it is not allowed to operate the direct drive mechanism 4 within the range where the inconvenience occurs; i.e., it is not allowed to widen the range of direct drive though this sacrifices the object for improving the fuel efficiency.